1. Field of the Invention
The present invention relates to cementitious products such as concrete, mortar, grout, and the like, and concrete products such as paving, paving blocks, concrete pipe, concrete blocks, cellular concrete, extruded concrete and roofing material, shot crete and concrete statuary; and more particularly to an improved cementitious composition and process for producing cemetitious products having improved resistance to water penetration and other deleterious elements and agents.
2. Description of Related Art
Concrete is a widely used engineering construction material, generally comprising a cementing or bonding substance, usually cement, and most commonly portland cement; aggregate, such as gravel, stone and/or sand; and water. Other cementitious products, such as mortar or grout are made by varying the type of aggregate employed. The cementing substance, particularly hydraulic cement, usually reacts chemically with water to form a hard, stonelike mass, which during concurrent mixing with aggregate, forms concrete, mortar and other cementitious products.
While cementitious products, such as concrete, particularly as used for pavement, bridges, walls, dams and the like, are relatively durable, they deteriorate over time, often due to the penetration of water into the product, particularly due to the porous nature of the product. Excess water is always used in a concrete mix in order to facilitate pouring and placement of the concrete. If the exact amount of water needed to hydrate the cement is used, the concrete would not be pourable or placeable. The excess water found in the mix is non-compressible and substantially evaporates from the concrete as it cures, and the resultant mass becomes porous as evaporation progresses. The porosity further diminishes the durability of the concrete, providing locations for water to penetrate the concrete. In climates where freezing temperatures periodically occur, the water in the product tends to freeze during such periods, and when frozen expands, often causing cracks, spalling and accellerated disintegration of the product. The deterioration is particularly noticeable where metal is used for reinforcement of the concrete products, for example, in the form of reinforcing mesh or rods, for example "rebars" in concrete pavement and the like. Over time, water penetrates through the concrete which corrodes metal reinforcement, often causing visible stains on the surface of the product, as well as weakening of the structure of the product.
In prior attempts to reduce water penetration, detergents have been mixed into the mixture of water, cementing substance and aggregate, but the result has been only marginally decreasing the porosity of the resulting product. Other known additives such as pozzolanic materials and metal salts of fatty acids provide only marginal improvement in water resistance, and also decrease the strength of the product during curing.
Quality concrete has surfactants added to the mix. Surfactants decrease the need for excess water, while making the concrete mix pourable as if the added amount of excess water was present. The pourability of the concrete mix is referred to as "slump". These surfactants are known as water-reducers, plasticizers and in some cases "super-plasticizers". When surfactants are introduced into the concrete, the result is a less porous and somewhat stronger product. The strength increase is attributed to lower water/cement ratio and decrease in porosity. While surfactants improve the resistance to water penetration, surfactants alone provide too little improvement to be considered a solution to the problem.
Another proposal to reduce water penetration has been the introduction into the composition of a glycol ester of a C.sub.8 -C.sub.22 fatty acid, such as the polyethyleneglycol ester of stearic acid, as in U.S. Pat. No. 4,878,948. The resulting product provides only incremental improvement in water penetration. Other attempts at reducing water penetration of cementitious products have utilized surface treatments, using such treatments as aqueous dispersions of film forming synthetic polymers and coagulants, film forming water-based, wax-free emulsions of a C.sub.4 linear polymer composition used for both wood and concrete surfaces, and paraffin wax in solvent coatings. These surface treatments are impractical with large surfaces, such as pavements, and are ineffective over a period of time due to wear and erosion of the coating due to climatic elements and ultraviolet deterioration.
Therefore, there is a need for compositions and a process for substantially improving the water resistance of cementitious products, which compositions and process do not decrease the strength and other properties of the products.